1. Field of the Invention
The present invention relates to a deflection device, which changes a propagation of an electromagnetic wave, and an apparatus, such as imaging apparatus using the same. In particular, the present invention relates to a deflection device which changes a propagation of an electromagnetic wave in a frequency domain of 30 GHz to 30 THz (in this specification, this is called a terahertz wave).
2. Description of the Related Art
Recently, engineering development using a terahertz wave is prosperous. In particular, applications to imaging are expected with taking advantage of transmission properties of the terahertz wave to various substances.
According to one proposal, organ imaging is performed using about 3.4 THz of terahertz wave (refer to OPTICS EXPRESS, Vol. 12, No. 9, pp. 1879, 2004 (Non-Patent Document 1)). In this proposal, an organ is placed in a focal position of a terahertz wave, and a terahertz wave image of the organ is obtained by moving the organ two-dimensionally.
In a terahertz wave area, development of an inexpensive and high-intensity light source and a highly sensitive detector is still insufficient. Therefore, it is hard to radiate electromagnetic wave on a whole object, to detect scattered waves, and to obtain an image, like in a visible and infrared area, or a radio wave area. In addition, a terahertz detector array is expensive and its sensitivity is also not sufficient. Hence, a method of converging and radiating a terahertz wave and detecting a reflected or transmitted wave from an object with a detector is performed widely.
However, since it is necessary in the method of Non-Patent Document 1 to move an imaging object two-dimensionally, it is hard to image a sample sensitive to vibration or acceleration. For example, when imaging a live creature, there is a possibility that the creature may move by moving a container into which the live creature is put.
In addition, the method of moving an imaging object needs a stage which can move a space which is large similarly to the object, so as to image a large object. On the other hand, in order to achieve imaging of a large object, it is also conceivable to adopt a system of deflecting a terahertz wave beam and making a focal position of a terahertz wave scanned on the object.
As beam deflection units, various units are proposed in areas of light and radio waves. What are known are a method of using a polygon mirror (refer to Japanese Patent Application Laid-Open No. H5-45600 (Patent Document 1)), a method of using an acousto-optic effect and an electro-optic effect, a method of using a diffraction grating (refer to Japanese Patent Application Laid-Open No. 2003-344791 (Patent Document 2)), and a method of using a holographic mirror (refer to Japanese Patent Application Laid-Open No. S60-68314 (Patent Document 3)).